The present invention relates to a machine having a rotor which is mounted so as to rotate about a rotation axis and contains a superconducting rotor winding, which is to be cooled or is cooled, and an uncooled rotor body. The rotor body has flattened parts on its outside so as to form outer regions respectively having a cross section at least similar to a circle segment, in which at least one coil of the rotor winding is arranged on a tensile retention holding device in at least one cryostat. A corresponding machine is disclosed by EP 1 261 114 A1.
Higher power densities, lower losses and further advantages can be achieved with a rotating superconducting excitation winding in superconducting technology machines such as synchronous motors and generators. The superconductor of the winding must in this case be cooled, and the winding needs to be enclosed in a high vacuum-isolated cryostat for thermal insulation reasons. The induced torque engages on the superconductor and must be forwarded to a warm rotor shaft via suitable transmission elements. Especially in large units, the centrifugal acceleration acting on the superconductor winding is a few thousand g (g=acceleration due to gravity) which has to be absorbed without damage to the superconductor material. Radial centrifugal forces and azimuthal magnetic forces need to be transmitted from the winding via suitable fastener to a mechanically stable rotor body, or a winding core or rotor core. This core may preferably be formed of a magnetically permeable material such as iron, so as to achieve an increase in the excitation field.
Embodiments of machines with a winding fastened directly on the cylindrical rotor body, which is formed of a nonmagnetic or magnetic material and which is at the winding temperature are known (DE 199 43 783 A1, U.S. Pat. No. 4,146,804 A1, WO 98/02953 A1). In corresponding large units, however, for example in power plant generators, the rotor body then comprises a large cooled mass of up to several tens of tonnes. This requires long cooling and warming times, stable elements for torque transmission to the warm shaft with a high heat flux in the cold region and a large vacuum cryostat which encloses the cold core and the winding.
Machines with rotors whose rotor body is not cooled to the temperature of the winding are also known (cf. EP 0 805 546 B1 or EP 0 690 550 B1). The windings are in this case of a so-called racetrack type and, together with a cryostat vacuum vessel, a cryoshield and cooling tubes carrying the coolant, are put into a groove machined in the warm rotor core. The groove is in this case closed externally by a comparatively massive closure element, via which forces acting on the winding during operation are absorbed and transmitted to the rotor core. Suspension straps or honeycomb structures in this case transmit forces between the winding and the shield, or between the shield and the closure element of the rotor core. At the ends, the winding cryostat is fed through radial bores in the rotor core. Nb3Sn is provided as a superconductor material for the windings, which is cooled with 10 K cold He gas. Details of the way in which the winding and the cryostat are designed in the respective groove are not disclosed by this related art. However, winding and mounting directly in the grooves requires considerable outlay.
The rotor body of the machine disclosed in the aforementioned EP 1 261 114 A1 is also uncooled. This rotor body has flattened parts on opposite longitudinal sides, so that outer regions with a cross section respectively similar to a circle segment are formed with respect to a cylindrical shape. In these outer regions, there is at least one cryostat for accommodating the conductors of the rotor winding to be cooled. At the ends, the winding cryostat is fed through radial bores in the rotor core. For mounting, the rotor core is designed in three parts; the magnetic core with flattened parts comprises the winding; fitted by bolts axially on both sides there are end pieces, which bear recesses for the winding on one side and the shaft ends of the rotor on the end facing outward. These end pieces may be formed of a nonmagnetic material such as stainless steel. At least one cold tensile element of a holding device, by which the radially opposite parts of the cryostat or cryostats and therefore the rotor winding are held, extends through the rotor body while being thermally insulated from it. Such fastening and holding of the rotor winding is elaborate. With this design of the machine, and especially its holding device, it is furthermore not sufficiently possible to absorb tangential forces which act during operation and particularly in the event of short circuits or other faults.